This invention relates to soluble coffee and more particularly to a method of extracting roasted coffee to produce a coffee extract.
In what may be termed the "standard" method of producing a coffee extract, roasted and ground coffee is contacted with an aqueous extraction liquid in the extraction columns of a percolator set. The percolator set generally is comprised of from 5 to 8 extraction columns connected in series, each column containing progressively fresher roasted and ground coffee. The extraction liquid enters the extraction column containing the most extracted roasted and ground coffee in the set (the spent stage), extracts soluble coffee solids from this coffee, and then passes successively through extraction columns containing progressively fresher coffee thereby increasing in soluble coffee solids concentration. After contacting the freshest or least extracted coffee in the set (the fresh stage), a pre-determined quantity of the liquid is drawn off as coffee extract which generally contains from about 20% - 35% by weight of soluble coffee solids. The quantity of extract drawn off is generally specified as a draw off factor (D.O.F.), i.e., the ratio of the weight of extract drawn off to the weight of roasted and ground coffee charged to the fresh stage extraction column.
After a coffee extract is drawn off from the fresh stage, the column containing the most extracted coffee (the spent stage) is discharged and charged with fresh roasted and ground coffee, thus becoming the fresh stage, i.e., the extraction column from which coffee extract is drawn off, in the next cycle. (Cycle is the time between successive draw-offs of coffee extract). Extraction liquid is then fed to the spent stage for this cycle, the coffee contained therein being the next most extracted coffee from the previous cycle. Successive cycles are continued in the above mannner such that a given charge of roasted and ground coffee becomes progressively more extracted with each successive cycle.
In split-extraction percolation, two feed streams of aqueous extraction liquid and two draw-offs of coffee extract are used. The percolator set is essentially divided into two parts, an atmospheric section and an autoclave section. The atmospheric section typically contains from one to four extraction columns containing the least extracted coffee and the autoclave section typically contains from two to five extraction columns containing the most extracted roasted coffee. As in standard percolation, the roasted and ground coffee flows in batches through the percolator set becoming progressively more extracted with each cycle.
An atmospheric aqueous extraction liquid is fed into the extraction column in the atmospheric section of the split-extraction percolator set containing the most extracted roasted and ground coffee for this section and flows through this atmospheric section contacting the coffee contained therein. Coffee extract, hereinafter called atmospheric coffee extract is drawn off from the fresh stage for this section, referred to hereinafter as the fresh stage of the atmospheric section. The atmospheric coffee extract contains the more aromatic and flavorful coffee solids extracted from roasted and ground coffee.
An autoclave aqueous extraction liquid is fed into the spent stage of the autoclave section of the split-extraction percolator set and an auatoclave coffee extract is drawn off from the column containing the least extracted coffee in this section, hereinafter termed the fresh stage for the autoclave section. In the autoclave section the temperatures and pressures within the extraction columns are significantly higher than in the atmospheric section of the split-extraction percolator set and the coffee solids in the autoclave coffee extract are largely autoclaved solids whereas the solids in the atmospheric coffee extract are largely atmospherically extracted solids.
A disadvantage with prior art split-extraction percolalation methods has been the low concentrations of coffee solids obtained from the atmospheric section of the percolator set. Such low concentrations necessitate further concentration of the atmospheric extract if it is to be dried separately prior to being added to separately dried autoclave coffee extract. Concentration of the atmospheric extract is normally accompanied by a loss of volatile aromatics and, hence, the final coffee product lacks to some degree the characteristic flavor and aroma of freshly brewed coffee. Prior art efforts to increase the soluble solids content in the atmospheric coffee extract are usually accompanied by a decrease in yield (ratio of weight of coffee solids in extract to weight of coffee loaded to fresh stage) for the atmospheric section if the draw-off is reduced or a decrease in quality if the temperature and pressure in the atmospheric section are increased. While some of the yield loss in the atmospheric section may be picked up when these coffees are extracted in the autoclave section, it is at the penalty of greater water loads to the evaporator which concentrates the autoclave extract product.